/Engine/Plugins/Runtime/GeometryProcessing/Source/DynamicMesh/Public/GroupTopology.h
Add the groups connected to all the GroupEdgeIDs to the GroupsOut list. This is not the either-side pair, but the set of groups on the one-ring of each connected corner.
void FindEdgeNbrGroups ( const [TArray](API\Runtime\Core\Containers\TArray)< int > & GroupEdgeIDs, [TArray](API\Runtime\Core\Containers\TArray)< int > & GroupsOut ) const